Process for reducing iron oxide fume formation during refining of steel

ABSTRACT

A PROCESS FOR THE FUMELESS REFINING OF STEEL IN WHICH A PARTICULATE METAL OXIDE IS SUSPENDED IN A CARRIER GAS, SUCH AS AIR, CONTAINING LESS THAN ABOUT 30% OXYGEN AND AT A RATIO OF LESS THAN ABOUT 3 CUBIC FEET OF GAS PER POUND OF OXIDE AND INJECTED INTO A MOLTEN FERROUS BATH AT A RATE SUFFICIENT TO PRODUCE A RAPID CARBON BOIL IN THE BATH.

United States Patent 3,749,567 PRQCESS FQR REDUCLIG EON OXIDE FUMEFGRhiATION DURING REFINING OF STEEL Stephen David Stephenson, Sheffield,England, and John Rees Morgan Richards, Cardiff, Wales, assignors toNational Research Development Corporation No Drawing.Continuation-in-part of abandoned appl cation Ser. No. 792,800, Ian. 21,1969. This application Jan. 11, 1971, Ser. No. 105,701 Claims priority,application Great Britain, Sept. 17, 1970, 44,413/70 Int. Cl. CZlc 7/00U.S. CI. 75-60 13 Claims ABSTRACT 0F THE DISCLOSURE A process for thefumeless refining of steel in which a particulate metal oxide issuspended in a carrier gas, such as air, containing less than about 30%oxygen and at a ratio of less than about 3 cubic feet of gas per poundof oxide and injected into a molten ferrous bath at a rate suflicient toproduce a rapid carbon boil in the bath.

This application is a continuation-in-part of our application Ser. No.792,800, filed Jan. 21, 1969, and now abandoned.

This invention relates to the refining of steels, including all gradesof plain carbon steels, low and high alloy steels, heat-resistingsteels, and stainless steels. More particularly, this invention relatesto a new and improved process for the fumeless refining of steels.

An essential step of refining in all steel-making processes (e.g.,convertor vessels, open-hearth furnaces, and electric furnaces) is theremoval of carbon by oxidation, together with other oxidisable elements,notably silicon, manganese, and phosphorus. Hydrogen and nitrogen arealso removed by the flushing of the carbon boil. The amount of carbon tobe removed and the rate of its removal governs the speed of the process,and also the final hydrogen and nitrogen contents, and accordingly it isusual to arrange for at least 0.20% of carbon to be removed fromferritic grades of steel, and 0.1% to 0.25% from austenitic stainlesssteels. This necessitates an adequately high carbon content in the bath,whatever the nature of the charge: steel scrap, hot metal, or cold pigiron, or various proportions of any of these. In the case of chargingwith 100% steel scrap, the high carbon content required for the refiningusually necessitates the addi tion of carbon, e.g., in the form ofcrushed electrodes, anthracite or coke.

Usually, the extent of refining is such as to leave the steel with therequired carbon content, but it is also known to refine a chargeinitially having a carbon content equal to or less than that required inthe refined steel, when the steel after refining inevitably has lessthan the required amount of carbon. In this case, it is normal torecarburize the refined steel to give it its required carbon content.

The rate of carbon removal varies according to the oxidation practiceadopted. In the case of ore boiling, i.e., the manual addition of ironore or millscale to the bath, which is essentially a slag-metalreaction, the reaction proceeds according to the equation:

cleaning equipment, it has several fundamental disadvantages:

3,749,567 Patented July 31, 1973 "ice In addition, the technique isgenerally inapplicable to stainless-steel charges.

Thus, the process which results in a carbon boil that is very slow andrelatively uneconomic has been considered unsatisfactory bysteel-makers, and their insistence for ever-increasing rates of carbonremoval has led to the development of processes to replace theore-boiling technique.

Of the processes that were developed, only one had provided the desiredrapidity of carbon removal, and prior to the present invention wasregarded by all as the only way of achieving the high rates of carbonremoval required by most steel-makers. This is the so-calledoxygenlancing technique, in which gaseous oxygen is injected into amolten bath. The result of such injection is that oxygen is rapidlydispersed throughout a melt, and this leads to rapid oxidation ofcarbon, i.e., a rapid carbon boil ensues with its beneficial flushingeffect on nitrogen and hydrogen.

Thus, in oxygen-lancing:

(i) the reaction is fast; and

(ii) in consequence of (i) the removal of hydrogen and nitrogen due tothe flushing action of the boil is not assured.

This technique as opposed to ore-boiling is suitable for stainless steelcharges.

Oxygen-lancing, therefore, meets all the requirements of thesteel-makers, but it has one serious disadvantage; the inevitable resultof oxygen-lancing is that large volumes of dense, brown iron-oxide fumesare emitted when the reaction is proceeding and expensive fume-cleaningequipment must be provided to prevent pollution of the surroundingatmosphere.

The cost of a fume-cleaning plant, however, has lead some steel-makersto sacrifice the rate of carbon removal achieved in oxygen-lancing byaccepting one of the other processes that were developed, such as theoxy-fuel burner (oil or gas). Such process can be controlled so thatlittle or no iron oxide fume is emitted, but the carbon-removal rate isgenerally slower than with oxygen-lancing. Thus, the cost is increased,particularly by the consumption of fuel and the increased'consumption ofoxygen, as well as the cost of providing cooling water for the burners.Moreover, the technique is limited to carbon steels and low alloysteels.

A principal object of the present invention, therefore, is to provide aneconomic and efiicient process for the rapid removal of carbon and otheroxidisable elements from a molten ferrous bath without the undueemission of the dense, brown iron oxide fumes commonly associated withoxygen-lancing. A further object is to provide such a process in whichthe required reduction in hydrogen and nitrogen contents will beassured.

According to the present invention, a process for refining a steelcomprises injecting into a molten ferrous bath a particulate oxide of ametal desired in the finished steel by means of a carrier gas containingfree or bound oxygen in such quantities and at a rate sufficient toreact with carbon to effect a rapid carbon boil, with evolution ofcarbon monoxide which flushes hydrogen and nitrogen from the bath, thevolume of evolved carbon monoxide in relation to the volume of oxygenavailable in the carrier gas under conditions prevailing in the bathbeing such as to give rise to a protective gaseous atmosphere above thebath which is non-oxidising for elemental iron, whereby production ofbrown iron oxide fume resulting from oxidation of elemental iron issubstantially inhibited.

Preferably, the carrier gas is one having an oxidising potential notgreater than oxygen-enriched air containing about 30% to about 35% byvolume, and it is further preferable that the carrier gas be utilised ata ratio of less than about 3 cubic feet of gas per pound of metal oxideinjected, so that the volume of carbon monoxide produced exceeds thevolume of oxygen injected to substantially inhibit the oxidation ofelemental iron by the gas and the production of brown iron oxide fumes.Thus, the ratio of carrier gas to oxide injected may be about 1 cubicfoot of air per pound of oxide.

It is to be understood that the foregoing general description and thefollowing detailed description are exemplary and explanatory but are notrestrictive of the invention.

Thus, the present invention has unexpectedly found that when the volumeof carrier gas is kept near the minimum required to inject the oxidethat a satisfactory carbon boil and a sufficient flushing of hydrogenand nitrogen is achieved without any or little production of obnoxious,brown iron oxide fumes.

The injection of the oxide by the use of a carrier gas, in accordancewith the present invention, promotes a sufiiciently high rate of carbonremoval for the removal of hydrogen and nitrogen from the bath to beassured during the carbon boil. At the same time, this method of carbonremoval has the most important advantage that the process can beconducted with the total elimination or minimisation of brown iron oxidefume.

Thus, the invention recognises for the first time that the volume ofcarbon monoxide resulting from the oxidation of carbon can be utilisedto bring about the substantial inhibition of the production of denseiron oxide fume in a refining process that has a rate of carbonelimination comparable with that of oxygen-lancing.

During a rapid carbon boil, irrespective of how it is brought about, theboil results in there being thrown from the surface of the melt a finespray or vapour of almost pure iron, it being the oxidation of this finespray or vapour that leads to the production of dense iron oxide fume.The fine spray or vapour only exists immediately above the bath becausebeyond that, there is coagulation into large particles which, if thenoxidised, would only be given an external coating and would, in allprobability, drop back into the slag. Therefore, when the carrier gascontains less than about 30% to 35% by volume of oxygen and the volumeof the carrier gas such as air, and is preferably substantially no morethan that required conveniently to bring about injection of theparticulate metal oxide, e.g., less than about 3 cubic feet per pound ofoxide, the volume of carbon monoxide produced by the reaction exceedsthe volume of oxygen injected and forms a blanket across the surface ofthe melt, the non-oxidising nature of which is not disturbed by therelatively small volume of gaseous oxygen from the carrier gas whichalso escapes from the melt. Thus, in the area of the furnace atmospherewhere the fine spray or vapour of iron is to be found, non-oxidisingconditions prevail, with the result that the process proceeds in thealmost complete absence of dense brown iron oxide fume.

As stated above, the volume of carrier gas should preferably at most beno more than about 3 cubic feet of gas per pound of metal oxide. Whenconditions permit, however, even smaller volumes such as 2 cubic feetand preferably one cubic foot of gas per pound of particulate oxide canbe employed.

The carrier gas employed for the purpose of this invention is one whichfunctions essentially as a carrier for the added metal oxide, the oxidebeing the principal agent for converting carbon in the bath into carbonmonoxide. The carrier gas, however, may participate to a small extent inthe oxidising process without departing from the process of the presentinvention and, therefore, may be active as far as oxidation reactionsare concerned by introducing some oxygen into the molten bath.Accordingly, carbon dioxide, air, or even oxygen-enriched air may beused as the carrier gas provided the oxygen content of the gas ismaintained below about 30% by volume and the volume of gas to oxide ismaintained within the limits described above. Gases containing higheramounts of oxygen even at minimum ratios of gas to oxide produceobjectionable iron oxide fume.

Additional advantages, particularly when using air as the carrier gasare:

(i) the process is relatively cheap;

(ii) the boil can be initiated and continued at a relatively low bathtemperature or the boil enriched and continued at any desiredtemperature by the maintained application of an external heat source tothe furnace;

(iii) in consequence of (ii), conditions can be created that areespecially favourable to the oxidation and removal of any desiredelements;

(iv) any desirable rate of carbon removal can be re-produced insuccessive operations;

(v) part of the oxide can be injected into the slag above the bath tobuild up slag iron which not only aids carbon removal from the bath butalso increases the metal yield, and

(vi) the injection does not give rise to the severe wear of therefractory of the furnace frequently occasioned by 0 lancing or byoxy-fuel burners, neither does it require the consumption of waterinvolved for the cooling of such burners.

The equipment for dispensing and injecting the oxide is cheap to installand operate. Thus, it may simply be a hopper having an outletcommunicating with the line for the carrier gas with means in the outletfor controlling the flow of powder to the line communicating with alance for injecting the powder into the bath. Preferably, the powder iscontrolled by providing means capable of pulsefeeding the powder intothe line for the carrier gas, the pulse-feeding may be carried out byproviding a valve in the form of a paddle wheel in the bottom of ahopper, the compartments formed between two vanes of the paddle wheeleffectively metering the supply of particulate oxide to the gas line.Preferably, two hoppers are provided, secured to a central spindle, oneof which is connected to the carrier gas line. When that hopper isempty, the hopper is simply disconnected from the line, the assemblyrotated about the spindle to bring the other, full hopper to theposition in which it can be connected to the carrier gas line, and whilethat hopper is emptying, the other hopper is filled.

The process admits of variation in the initial carbon content of thebath. Thus, if the carbon content of the charge from which the bath isformed is in excess of that required in the refined steel, the injectionis continued until carbon has been removed by oxidation to leave anamount equal to that required in the final steel, by which time hydrogenand nitrogen have been appreciably reduced and other undesirableelements such as silicon, manganese, and phosphorus have all beenoxidised to the desired level. Again, if there is a lower carbon contentof the charge from which the bath is formed than is sufficient for thefinal content to be that required in the refined steel, the injection iscontinued until carbon has been removed by an amount sufiicient toassure removal of hydrogen and nitrogen and oxidation of any otherundesirable elements, and the refined steel is then recarburised inknown manner, to give it its required carbon content.

The technique is applicable to all the grades of steel mentioned above.Depending on the particular steel to be produced, suitable oxides arethose of iron, nickel, chromium, molybdenum, copper, cobalt andtungsten. For example, for carbon steels, iron oxide is used, e.g., inthe form of millscale, iron ore, or iron oxide dust fro-m fumecleaningplants; and for stainless steel, oxides of nickel, chromium, molybdenum,copper, cobalt or tungsten, or any combination of these, possibly withan iron oxide also both to promote the oxidation reactions and toprovide a .5 cheaper source for at least part of the metal constituentsof the steels.

Particle as used in the specification and claims, is intended to embraceall useful grades from relatively coarse, granular grades (say 5.75 mm.grain size) down to very fine grades. Of course, the metal oxide cannotbe so coarse as to be incapable of being blown through the lance nor canit be so very fine that it would remain entrained in the gas and simplybe blown into the furnace atmosphere. The following has proved to be anadequate range of gradings:

100% less than 6.35 mm.; not more than approximately 30% less than0.0104 mm.

Example 1.Carbon steel A 4-ton electric arc furnace was charged withsteel scrap and heated to a temperature of 1550 C., a slag being formedon the bath in known manner. The bath was then ready to be oxidised, andpowdered millscale with the following grading':

was injected into the bath for two (2) minutes at 50 lbs./ minute by alance immersed in the bath, using compressed air as the carrier gas. Thetotal volume of air used was 100 cubic feet, when converted to standardtemperature and pressure (S.T.P.).

The bath was sampled immediately before and immediately after the oxideinjection and was found to contain (percent by weight):

Mn Si S P Ni Cr N2 p.p.m.

No'rE.l=Before injection; 2=After injection.

This steel was required to have 0.24% CA and accordingly required norecarburisation. The bath was then slagged off, de-oxidised, a reducingslag made up, in known manner and finally tapped.

The rate of carbon removal was such that nitrogen and hydrogen wereappreciably reduced as can be seen from the above table and theoxidation proceeded with no visible brown fume from the bath.

Example 2.Carb0n steel The procedure as outlined in Example 1 wasfollowed and the bath again oxidised by injecting millscale powdered to5 BSS with compresssed air as the carrier gas, but in this case, 100lbs/minute of powder was injected for 3 /2 minutes, utilising a total of375 cubic feet of air at S.T.P. The oxidation proceeded with no visiblebrown fume from the bath.

Sampling of the bath immediately before and after the injection showedthe bath to contain (percent by weight):

0 Mn S P N2 p.p.m.

NorE.1=Beio1-e injection; 2=After injection.

In this case, the steel was required to have 0.30% C and accordingly,the steel was recarburised by adding 280 lbs. of pig iron known tocontain 4% C.

Example 3. Austenitic stainless steel The same procedure as outlined inExample 1 was fol lowed, on /2-ton charge in an electric arc furnace,and the bath again oxidised by injecting millscale powdered to 5 BSS (asin Example 1) with compressed air as the carrier gas. The powder wasinjected at a rate of 20 lbs./ minute for 3 /2 minutes, utilising atotal of 105 cubic feet of air at S.T.P. The oxidation proceeded with novisible brown fume from the bath.

Sampling of the bath immediately before and after oxidation showed thebath to contain (percent by weight) C Si S P Ni Cr N No'rE.1=Beforeinjection; 2=After injection.

The table shows clearly the reduction by oxidation of the oxidisableelements. The Cr content of the steel has been reduced to a level toolow for the required final analysis of the steel, and accordingly,additions of reducing agents, such as ferro-silicon are made to the slagwhereby Cr is released from the slag back to the bath. After sampling,the Cr content was found to have increased to 14%.

The bath was then slagged off and a reducing slag made up and finallytapped. If it had been the case that the other alloying elements neededto be increased, suitable additions of such elements could be made afterthe reducing slag had been made up.

Example 4.Austenitic stainless steel 0 Si S P Mn Cr Ni Mo N 0TE.1=Beforeinjection; 2=After injection.

During the oxidation stage, the increase in nickel content showed thatof the nickel of the nickel oxide had been recovered. The chromium (andother alloying elements) were modified to suit the requirement of thefinal steel as explained in Example 3.

Example 5.5% chrome alloy steel The same procedure as outlined inExample 1 was followed, using a mixture of 50% chromite sand (crushedchrome ore) and 50% millscale, both graded in similar manner to themillscale of Example 1. The oxidation proceeded with no visible brownfume given off from the bath.

Immediately before oxidation the bath was sampled and found to contain0.75% carbon and 6.18% chromium. After oxidation, the bath contained0.65% carbon and 5.80% chromium, well within the 5% to 6% chro- 8Examples 8 and 9 Examples 8 and 9 are carried out to illustrate thelimit required on the amount of oxygen that should be in the carrier gasto prevent the production of brown fume.

mium required in the final steel. The chromite sand has, 5 i In eachfzxample Powdered {ninscale is into therefore, provided a cheap sourceof chromium for the reslstor furnace usuig comgressed an as the h d h ifI if t th d b carrier gas. The air is then enriched with oxygen up to fan as e i 0 8 re uc y the point when brown oxide fume is first observedand non of the chrommm, making unnecessary the addition 10 thepfircentage of oxygen in the carrier gas at that point of expensivechromium at the reducing stage. i e o d d i th following table:

Total 7 Oxygen volume 01 Percent flow rate Volume oxygen oxygen in Ftfiof Millscale Air at pt. of Total gas of oxygen at pt.oi carrier carrierflow rate, flow rate, of fuming, flow rate, in air, fuming gas at pt.gas/lb. of Example 1b.]nnn. ftfi/n'un. ftfijmin ti /min. ftfilmin.tt./min. of turning millscale Example 6.Carbon steel From the foregoingtable it can be seen that at various An electric arc furnace was chargedwith 37.95 tons of flow mites 9 10 to uni/minute of.mfllscale and atScrap and heated to a temperature of 1,5003 C; a Slag gas/oxide ratiosof about 1:1, that fuming began to ocbeing formad in a known manner. Thebath was them 2 our when the oxygen content of the gas approached aboutready to be oxidised and fines from an iron ore sinter plant by volumewhich had passed through A" (6.35 mm.) sieve were in- Example 10.-Carbonsteel jected into the bath for 3 minutes at a rate of 373 lbs./ minuteby a lance immersed in the bath. 450 cubic feet A ti rod furnace was l f2 1th stleal at S.T.P. of compressed air were used as a carrier gas 30Zg i: g i ffi i i .f 3% at a pressure of 50 p.s.i. The oxidationproceeded with mm on e a now anner a no visible brown fume from the bathwas t ..n ready to be oxidised and powdered millscale,

The bath was sampled immediately before and immegenerally 9 the giadmgreferred to m prevlou? examdiately after injection and was found tocontain (percent g .mlected mm the .bath for (one) mmute. at b Weight):s./n 11nute by a lance mmersed in the bath, using y carbon dioxide asthe carr1er gas. The total volume of carbon dioxide was 50 cubic feetwhen converted to S.T.P. 1 s s P o N C h n 1 r 2 The bath was sampledimmediately before and immeg-g g 8-22 8-8; 8-3:; 88%; 3% 8 3% diatelyafter the oxide injection and was found to con- 40 tain (percent byweight). The bath was then slagged off, de-oxidised, a reducing slagmade up in known manner and finally tapped. 0 M11 31 S P 1 1.03 .65 .010.024 .035 Example 7 2 .35 .23 .01 .036 .024 A 240-ton open-hearthfurnace was charged with 145 N0TE 1=BefOre injection; 2=Mterinjecfiomtons of scrap and 95 tons of hot metal from a blast furnace. At melt-outthe metal contained 0.70% carbon which 1 Steel was bljought to E carbonComm]; it the dropped to 0.45% 43 minutes after melt-out. At this pointmm and, accordmgly, reqmred 9 recarbunsanpn- The 3,136 lbs. of ironoxide powder were injected with 1,400 bath Was f Slagged de-mildlsed, al'educmg cubic feet at S.T.P. of air at a pressure of lbs/square 50 madeup In known manner and finally pp f inch by a lance immersed in themetal The rate of carbon removal was such that nltrogen and noxidehadthe following grading; hydrogen were appreciably reduced, and theoxidation p b proceeded with no visible brown fume from the bath.Particle Size Percent y The invention in its broader aspects is notlimited to 33904590 the specific details shown and described anddepartures may be made from such details without departing from106041025 the principles of the invention and without sacrificing its0325-0318 chief advantages. (1018-0015 11-6 What We claim 1. A processfor the refining of steel in which the pro- 1 7 5 duction of brown11'011 oxide fume dlllll'lg decarburization Samples taken from the bathat various times during 15 substflntlany feduqed Comprising inlfictiflginto a molten the refining period gave the following results: ferrousbath contaimng carbon, a particulate oxide of a.

metal desired in the finished steel, said oxide being in- Percent 5jected by means of a carrier gas and at a rate sufiicient to SamplePercent C C oxidize the carbon in the bath and effect a rapid carbon Atmelt-out 0.70 boil with the evolution of carbon monoxide and the flushgglg giigfggfl g g: g-f f' r ing'of hydrogen and nitrogen from the bath,said carrier 513/ rm'nslafter melt-out Finish 11139011011 1 gas beingused in an amount suflicient to inject the deg gfif g gfggfi fi .17 7sired rate of oxide but having an oxidizing potential not greater thanoxygen-enriched air containing about 35% The steel was then tapped inthe usual manner and cast oxygen by volume so that the carrier gas willnot sub} into ingots. stantially influence the rate of oxidation ofcarbon from The oxidation proceeded with no visible brown fume the bathand so that the particulate metal oxide will be from the bath. theprincipal oxdizing agent for the carbon, whereby the evolving carbonmonoxide will create a non-iron oxidizing atmosphere above the bath andsubstantially reduce the production of the brown iron oxide fumes duringthe decarburizing process.

2. The process of claim 1, wherein the carrier gas is selected from thegroup consisting of air, oxygen-enriched air containing up to 35% oxygenby volume, carbon dioxide, or mixtures thereof.

3. The process of claim 1, wherein said carrier gas is used at a ratioof less than about three (3) cubic feet of gas per pound of metal oxideinjected.

4. The process as in claim 3, wherein said carrier gas is used at aratio of about one (1) cubic foot of gas per pound of metal oxideinjected.

5. The process of claim 1, wherein the bath has a carbon content inexcess of that required in the final steel and the injection iscontinued until carbon has been reduced down to an amount equal to thatrequired in the final steel.

6. The process of claim 1, wherein the bath has a carbon content lowerthan is sufiicient for the final content to be that required in thefinal steel and the injection is continued until carbon has been reducedby an amount sufiicient to assure removal by oxidation of otheroxidizable elements in the bath, the refined steel then beingrecarburized to give it its required carbon content.

7. The process of claim 1, wherein particulate iron oxide is injectedinto the molten bath.

8. The process of claim 7, wherein the iron oxide is in the form ofmillscale, iron ore, or iron oxide dust.

9. The process of claim 7, wherein part of the iron oxide is injectedinto the slag above the bath.

10. The process of claim 1, wherein the steel is a stainless steel.

11. A process for the refining of carbon steel in which the productionof brown iron oxide fume during decarburization is substantially reducedcomprising injecting into a molten ferrous bath containing carbon,particulate iron oxide suspended in air as a carrier gas for the oxide,said oxide being injected at a rate sufiicient to oxidize the carbon inthe bath and effect a rapid carbon boil with the evolution of carbonmonoxide and the flushing of hydrogen and nitrogen from the bath, andsaid carrier air being used at a ratio of less than about three 3) cubicfeet of air per pound of iron oxide injected, so that the air will notsubstantially influence the rate of oxidation of carbon from the bathand so that the iron oxide will be the principal oxidizing agent for thecarbon, whereby the evolving carbon monoxide will create a non-ironoxidizing atmosphere above the bath and substantially reduce theproduction of brown iron oxide fumes during the decarburizing.

12. The process of claim 11, wherein said carrier air is used at a ratioof about one (1) cubic foot of air per pound of iron oxide injected.

13. The process of claim 11, wherein the iron oxide is in the form ofmillscale, iron ore, or iron oxide dust.

References Cited UNITED STATES PATENTS 2,991,173 7/1961 Trentini et a156 3,567,202 3/1971 Mercatoris et al 75--60 2,593,505 4/1952 Wagstaff7551 2,502,259 3/1950 Hulme 75-51 FOREIGN PATENTS 401,094 11/ 1933 GreatBritain 7551 607,209 8/ 1948 Great Britain 7551 861,238 2/1961 GreatBritain 7552 933,414 8/1963 Great Britain 7560 956,939 4/ 1964 GreatBritain 7560 970,858 9/1964 Great Britain 7560 777,381 6/ 1957 GreatBritain 7560 970,990 9/1964 Great Britain 7552 L. DEWAYNE RUTLEDGE,Primary Examiner W. R. SATTERFIELD, Assistant Examiner US. Cl. X.R.

